Plants annual, 30-60 cm tall. Stem erect, branched in upper part; branchlets ascending, slender. Leaves subopposite with petiole 2.5-4.5 cm in lower part of stem, alternate and shortly petiolate or subsessile in upper part of stem; leaf blade pale green abaxially, green adaxially, ovate or ovate-oblong, 2.5-9 × 1.5-3 cm, membranous, sparsely puberulent or subglabrous, lateral veins 4-6 pairs, inconspicuous, base broadly cuneate or cordate in lower leaves, but cordate-amplexicaul in upper leaves, margin coarsely retuse, sometimes undulate, rarely nearly entire, apex obtuse or rounded. Inflorescences in upper leaf axils, 1-or 2-flowered; peduncles shorter than leaves, 3-4 cm. Pedicels 1.3-1.5 cm, bracteate above middle; bracts persistent, ovate-lanceolate, ca. 3 mm, leathery. Flowers purple-red, 2.5-3 cm deep. Lateral sepals 2, obliquely ovate, 10-12 × 8-9 mm, abaxial midvein not thickened, 5-veined. Lower sepal saccate, 2-2.5 cm deep, abruptly narrowed into a very short, erect or curved spur ca. 2 mm, or almost without spur; mouth oblique, 1.5-2 cm wide. Upper petal orbicular, ca. 1.5 cm in diam., apex rounded, abaxial midvein thickened; lateral united petals shortly clawed or ± clawed, 2.5-3 cm, 2-lobed; basal lobes ovate-orbicular, apex emarginate; distal lobes broadly dolabriform-falcate, apex acuminate; auricle inflexed, narrow. Filaments linear, 3-4 mm; anthers obtuse. Ovary fusiform, 4-5 mm, rostellate. Capsule linear, 3-3.5 cm. Fl. Jul-Aug, fr. Sep.
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